This disclosure is in the field of desalination processes and, more particularly, desalination processes that do not rely upon a heat exchanging surface or pretreatment to meet feed water specifications.
Current desalination processes are complicated, expensive, and typically require extensive water pretreatment to ensure the proper quality of the boiler feed water. In some cases, the cost of pretreatment exceeds the cost of the actual boiling processes. U.S. Pat. No. 8,652,304 B2 (“Nazzer”) discloses a method of extracting dissolved or undissolved solids from a mixture of water and a process liquid or stream. The mixture is introduced into a mixing zone within or upstream of a separation vessel where it is further mixed with a recycle fluid extracted from a liquid pool zone of the separator vessel and pumped through a heat exchanger.
Vaporization occurs in this mixing zone (where more than 99% of the volatile components of the feed stream are vaporized). The resulting stream is then transferred to the separator vessel in which the vapor is separated, with the solid and liquid components falling into the liquid pool zone of the separator vessel. A portion of these solids and liquids that bond to these solids then passes through a stripping zone of the separator vessel. Water residing within the stripping zone displaces the liquids bound to the solids and an aqueous waste stream with dissolved or nondissolved solids results.
Because this method requires a mixing zone for vaporization outside of the liquid pool, the required equipment is difficult to design and prone to scaling and plugging. The method also does not allow for vaporization within the liquid pool and requires the heating medium—i.e., the recycle fluid, immiscible with the process stream and lighter than the water in the stripping zone—to be recycled at a rate of at least ten times that of the process feed rate. This high recycle rate is required because the method must limit the temperature difference between the recycle fluid and the feed water stream in order to avoid thermal degradation effects.
Last, the method requires a stripping zone for solids removal. A stripping zone is prone to corrosion because of unvaporized (solids) components from the feed water stream. The stripping zone also presents safety concerns due to the risk of higher temperature oil contacting water. To reduce the safety concern, the oil must be cooled before it touches the water in the stripping zone, but cooling the oil increases its viscosity and ineffective solids separation results.